At least some of the memory transistors included in a first memory string are commonly connected to first conductive layers that are connected to at least some of the memory transistors included in a second memory string connected to the same third and fourth conductive layers as the first memory string. At least one of either the memory transistors or the back-gate transistor in the first memory string and at least one of either the memory transistors or the back-gate transistor in the second memory string are connected to the independent first or fifth conductive layers, respectively.
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18. A semiconductor storage device comprising:
a memory cell array having a plurality of memory strings arranged therein, each of the memory strings including a plurality of electrically rewritable memory transistors and selection transistors operative to select the memory transistors;
a word line connected to a control gate of a respective one of the memory transistors;
a bit line connected to one end of a respective one of the memory strings; and
a source line connected to the other end of a respective one of the memory strings,
at least some of the memory transistors included in a first memory string being commonly connected to the word lines connected to at least some of the memory transistors included in a second memory string, the first memory string being one of the memory strings that is connected to one of the bit lines and one of the source lines, the second memory string being another one of the memory strings that is adjacent to the first memory string and connected to the same bit line and source line,
at least one of the transistors in the first memory string and at least one of the transistors in the second memory string being configured to be controlled in its conduction independently of each other.
17. A semiconductor storage device comprising:
a memory cell array having a plurality of memory strings arranged therein, each of the memory strings including a plurality of electrically rewritable memory transistors and selection transistors operative to select the memory transistors,
each of the plurality of memory strings comprising:
a body semiconductor layer having a columnar portion extending in a vertical direction to a substrate;
an electric charge storage layer formed to surround a side surface of a respective one of the columnar portions;
a first conductive layer formed to surround a side surface of the columnar portion as well as the electric charge storage layer, and functioning as a word line connected to a control electrode of a respective one of the memory transistors;
a second conductive layer formed on a side surface of the columnar portion via an insulation film, and functioning as a selection gate line connected to a control electrode of a respective one of the selection transistors;
a third conductive layer arranged with a first direction taken as its longitudinal direction, connected to one end of a respective one of the memory strings, and functioning as a bit line; and
a fourth conductive layer arranged with the first direction taken as its longitudinal direction, connected to the other end of a respective one of the memory strings, and functioning as a source line,
the memory transistors included in a first memory string being commonly connected to the first conductive layers connected to the memory transistors included in a second memory string, the first memory string being one of the memory strings that is connected to a pair of the third conductive layer and the fourth conductive layer, the second memory string being another one of the memory strings that is connected to the same third and fourth conductive layers and adjacent to the first memory string,
the selection transistors in the first memory string and the selection transistors in the second memory string being connected to the independent second conductive layers, respectively.
1. A semiconductor storage device comprising:
a memory cell array having a plurality of memory strings arranged therein, each of the memory strings including a plurality of electrically rewritable memory transistors and selection transistors operative to select a memory transistor,
each of the plurality of memory strings comprising:
a body semiconductor layer having first and second columnar portions extending in a vertical direction to a substrate, and a joining portion formed to join the lower ends of the first and second columnar portions;
an electric charge storage layer formed to surround a side surface of a respective one of the columnar portions;
a first conductive layer formed to surround a side surface of a respective one of the columnar portions as well as the electric charge storage layer, and functioning as a word line connected to a control electrode of a respective one of the memory transistors;
a second conductive layer formed on a side surface of a respective one of the columnar portions via an insulation film, and functioning as a selection gate line connected to a control electrode of a respective one of the selection transistors;
a third conductive layer arranged with a first direction taken as its longitudinal direction, connected to one end of a respective one of the memory strings, and functioning as a bit line;
a fourth conductive layer arranged with the first direction taken as its longitudinal direction so as to be inserted between a plurality of the third conductive layers, connected to the other end of a respective one of the memory strings, and functioning as a source line; and
a fifth conductive layer formed on a side surface of the joining portion via an insulation film, and functioning as a control electrode of a back-gate transistor, the back-gate transistor being one of the selection transistors that is formed at one of the joining portions,
at least some of the memory transistors included in a first memory string being commonly connected to the first conductive layers connected to at least some of the memory transistors included in a second memory string,
the first memory string being one of the memory strings that is connected to adjacent ones of the third and fourth conductive layers,
the second memory string being another one of the memory strings that is connected to the same third and fourth conductive layers that the first memory string is connected to,
at least one of the memory transistors or the back-gate transistor in the first memory string and at least one of the memory transistors or the back-gate transistor in the second memory string being connected to the independent first or fifth conductive layers, respectively.
2. The semiconductor storage device according to
the first and second memory strings are commonly connected to each other with same ones of the first conductive layers only at either the memory transistors positioned along the first columnar portions or at the memory transistors positioned along the second columnar portions.
3. The semiconductor storage device according to
4. The semiconductor storage device according to
5. The semiconductor storage device according to
6. The semiconductor storage device according to
7. The semiconductor storage device according to
8. The semiconductor storage device according to
9. The semiconductor storage device according to
the fourth conductive layer has a larger wiring width than that of the third conductive layer, and
two of the memory strings are arranged below the fourth conductive layer along a second direction orthogonal to the first direction.
10. The semiconductor storage device according to
the first and second memory strings are commonly connected to each other with same ones of the first conductive layers only at either the memory transistors positioned along the first columnar portions or at the memory transistors positioned along the second columnar portions.
11. The semiconductor storage device according to
12. The semiconductor storage device according to
13. The semiconductor storage device according to
14. The semiconductor storage device according to
the joining portion is arranged with the first direction taken as its longitudinal direction, and a plurality of the joining portions that are arranged along a second direction orthogonal to the first direction are positioned so that their respective ends are in line with each other,
a plurality of the fifth conductive layers are formed in a stripe pattern with the first direction taken as their longitudinal direction, and
the first and second memory strings are configured so that all of the memory transistors and the selection transistors included in the first and second memory strings are connected to the common first and second conductive layers, and that the back-gate transistors included in the first and second memory strings are connected to the different fifth conductive layers and controlled independently of each other.
15. The semiconductor storage device according to
16. The semiconductor storage device according to
19. The semiconductor storage device according to
each of the plurality of memory strings comprising:
a body semiconductor layer having first and second columnar portions extending in a vertical direction to a substrate, and a joining portion formed to join the lower ends of the first and second columnar portions;
an electric charge storage layer formed to surround a side surface of a respective one of the columnar portions;
a first conductive layer formed to surround a side surface of a respective one of the columnar portions as well as the electric charge storage layer, and functioning as a word line connected to a control electrode of a respective one of the memory transistors;
a second conductive layer formed on a side surface of a respective one of the columnar portions via an insulation film, and functioning as a selection gate line connected to a control electrode of a respective one of the selection transistors;
a third conductive layer arranged with a first direction taken as its longitudinal direction, connected to one end of a respective one of the memory strings, and functioning as a bit line;
a fourth conductive layer arranged with the first direction taken as its longitudinal direction so as to be inserted between a plurality of the third conductive layers, connected to the other end of a respective one of the memory strings, and functioning as a source line; and
a fifth conductive layer formed on a side surface of the joining portion via an insulation film, and functioning as a control electrode of a back-gate transistor, the back-gate transistor being one of the selection transistors that is formed at one of the joining portions.
20. The semiconductor storage device according to
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This application is based on and claims the benefit of priority from prior Japanese Patent Application No. 2009-212330, filed on Sep. 14, 2009, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an electrically rewritable non-volatile semiconductor storage device.
2. Description of the Related Art
Conventionally, LSIs are formed by integration of devices in a two-dimensional plane on the silicon substrate. Although the dimension for each device is commonly reduced (refined) to increase memory storage capacity, recent years are facing challenges in such refinement from the viewpoint of cost and technology. Such refinement requires further improvements in photolithography technology. However, the costs of lithography process are ever increasing. In addition, if such refinement is accomplished, it is assumed that physical improvement limit, such as in breakdown voltage between devices, would be reached unless driving voltage can be scaled. That is, it is likely that difficulties would be encountered in device operation itself.
Therefore, such semiconductor storage devices have been proposed recently where memory cells are arranged in a three-dimensional manner to achieve improved integration of memory devices.
One of the conventional semiconductor storage devices where memory cells are arranged in a three-dimensional manner uses transistors with a cylinder-type structure (see, for example, Japanese Patent Laid-Open No. 2007-266143). Those semiconductor storage devices using transistors with the cylinder-type structure are provided with multiple conductive layers corresponding to gate electrodes and pillar-like columnar semiconductors. Each columnar semiconductor serves as a channel (body) part of a respective transistor. Memory gate insulation layers are provided around the columnar semiconductors. Such a configuration including these conductive layers, columnar semiconductors, and memory gate insulation layers is referred to as a “memory string”.
In these conventional semiconductor storage devices with three-dimensional structures, those memory strings to be read at the same time have one ends connected to respective bit lines and the other ends connected to a common source line. This configuration has a problem that changes in the potential (potential floating) of the source line due to read current become larger and the read current becomes smaller as more memory cells are integrated and more memory strings are to be read at the same time, which results in a longer reading time. This configuration is also problematic in providing a sufficient read margin because the amount of potential floating of the source line varies depending on the position in the memory cell array, causing variations in read current.
One aspect of the present invention provides a semiconductor storage device comprising: a memory cell array having a plurality of memory strings arranged therein, each of the memory strings including a plurality of electrically rewritable memory transistors and selection transistors operative to select a memory transistor, each of the plurality of memory strings comprising: a body semiconductor layer having first and second columnar portions extending in a vertical direction to a substrate, and a joining portion formed to join the lower ends of the first and second columnar portions; an electric charge storage layer formed to surround a side surface of a respective one of the columnar portions; a first conductive layer formed to surround a side surface of a respective one of the columnar portions as well as the electric charge storage layer, and functioning as a word line connected to a control electrode of a respective one of the memory transistors; a second conductive layer formed on a side surface of a respective one of the columnar portions via an insulation film, and functioning as a selection gate line connected to a control electrode of a respective one of the selection transistors; a third conductive layer arranged with a first direction taken as its longitudinal direction, connected to one end of a respective one of the memory strings, and functioning as a bit line; a fourth conductive layer arranged with the first direction taken as its longitudinal direction so as to be inserted between a plurality of the third conductive layers, connected to the other end of a respective one of the memory strings, and functioning as a source line; and a fifth conductive layer formed on a side surface of the joining portion via an insulation film, and functioning as a control electrode of a back-gate transistor, the back-gate transistor being one of the selection transistors that is formed at one of the joining portions, at least some of the memory transistors included in a first memory string being commonly connected to the first conductive layers connected to at least some of the memory transistors included in a second memory string, the first memory string being one of the memory strings that is connected to adjacent ones of the third and fourth conductive layers, the second memory string being another one of the memory strings that is connected to the same third and fourth conductive layers that the first memory string is connected to, at least one of the memory transistors or the back-gate transistor in the first memory string and at least one of the memory transistors or the back-gate transistor in the second memory string being connected to the independent first or fifth conductive layers, respectively.
In addition, another aspect of the present invention provides a semiconductor storage device comprising: a memory cell array having a plurality of memory strings arranged therein, each of the memory strings including a plurality of electrically rewritable memory transistors and selection transistors operative to select the memory transistors, each of the plurality of memory strings comprising: a body semiconductor layer having a columnar portion extending in a vertical direction to a substrate; an electric charge storage layer formed to surround a side surface of a respective one of the columnar portions; a first conductive layer formed to surround a side surface of the columnar portion as well as the electric charge storage layer, and functioning as a word line connected to a control electrode of a respective one of the memory transistors; a second conductive layer formed on a side surface of the columnar portion via an insulation film, and functioning as a selection gate line connected to a control electrode of a respective one of the selection transistors; a third conductive layer arranged with a first direction taken as its longitudinal direction, connected to one end of a respective one of the memory strings, and functioning as a bit line; and a fourth conductive layer arranged with the first direction taken as its longitudinal direction, connected to the other end of a respective one of the memory strings, and functioning as a source line, the memory transistors included in a first memory string being commonly connected to the first conductive layers connected to the memory transistors included in a second memory string, the first memory string being one of the memory strings that is connected to a pair of the third conductive layer and the fourth conductive layer, the second memory string being another one of the memory strings that is connected to the same third and fourth conductive layers and adjacent to the first memory string, the selection transistors in the first memory string and the selection transistors in the second memory string being connected to the independent second conductive layers, respectively.
Still another aspect of the present invention provides a semiconductor storage device comprising: a memory cell array having a plurality of memory strings arranged therein, each of the memory strings including a plurality of electrically rewritable memory transistors and selection transistors operative to select the memory transistors; a word line connected to a control gate of a respective one of the memory transistors; a bit line connected to one end of a respective one of the memory strings; and a source line connected to the other end of a respective one of the memory strings, at least some of the memory transistors included in a first memory string being commonly connected to the word lines connected to at least some of the memory transistors included in a second memory string, the first memory string being one of the memory strings that is connected to one of the bit lines and one of the source lines, the second memory string being another one of the memory strings that is adjacent to the first memory string and connected to the same bit line and source line, at least one of the transistors in the first memory string and at least one of the transistors in the second memory string being configured to be controlled in its conduction independently of each other.
Embodiments of the present invention will now be described in detail below with reference to the accompanying drawings.
Referring now to the drawings, a non-volatile semiconductor storage device according to embodiments of the present invention will be described.
At first, a first embodiment of the present invention will be described in detail below with reference to the drawings, such as
The non-volatile semiconductor storage device 100 comprises a memory cell array 12 that has memory transistors for storing data arranged in a three-dimensional manner. The memory cell array 12 includes memory strings MS arranged in a matrix form. Each memory string MS has a plurality of memory transistors MTr and a back-gate transistor BGTr connected in series in U-shape in a lamination direction, as well as a drain-side selection transistor SDTr and a source-side selection transistor SSTr connected to each end. As described below, the memory transistors MTr are MONOS-type transistors. The memory transistors MTr, which are formed to be aligned in the lamination direction, have their control gate electrodes connected to the word lines WL that are laminated in the lamination direction with interlayer insulation films (not illustrated) sandwiched therebetween.
In addition, each drain-side selection transistor SDTr and each source-side selection transistor SSTr have their gate electrodes connected to respective selection gate lines SG. The selection gate lines SG are formed with a row direction (second direction) taken as their longitudinal direction, and arranged at a certain pitch in a column direction (first direction). Additionally, in this embodiment, both bit lines BL and source lines. SL are formed in parallel to each other with the column direction (first direction) taken as their longitudinal direction. The bit lines BL and the source lines SL are arranged to alternate with one another in the row direction.
As illustrated in
As illustrated in
In addition, as illustrated in
In addition, word lines WLm are arranged at the same arrangement pitch as that of the columnar portions CLmn so that each of the word lines surrounds one of the columnar portions CLmn via an insulation film. As illustrated in
In addition, as illustrated in
In addition, each word line WLmn is formed to surround the side surface of a columnar portion CLmn and an electric charge storage layer EC. The columnar portions CLmn and the corresponding joining portion JPmn are formed in a tubular form having a hollow portion HI therein, which is filled with an insulation film I such as a silicon oxide film. The columnar portions and the corresponding joining portion may also be filled up with, including their interior parts, a conductive film such as polysilicon, without such a hollow portion HI.
In addition, selection gate lines SG are formed above the word lines WLm as wirings for connection with the selection transistors SDTrmn and SSTrmn. Each of the selection gate lines SG is formed to surround one columnar portion CLmn via an insulation film GI (see
Each back-gate transistor BGTrmn includes a joining portion JPmn, an ONO layer NL (an electric charge storage layer EC), and the back-gate line BG. Those ends of the back-gate line BG that come in contact with the ONO layers NL function as the control gate electrodes of the back-gate transistors BGTrmn.
Referring now to the plan view of
As described above, the bit lines BL are arranged at a certain arrangement pitch with the column direction taken as their longitudinal direction. The source lines SL are arranged at the same arrangement pitch as that of the bit lines BL with the column direction also taken as their longitudinal direction, so that each source line is inserted between two bit lines BL. That is, the bit lines BL and the source lines SL are arranged to alternate with one another in the row direction.
As illustrated in
In addition, the one selection gate line SG shared by the memory strings MS0 and MS1 functions as a drain-side selection gate line SGD in the memory string MS1 and as a source-side selection gate line in the memory string MS0. The memory strings MS are arranged in this zig-zag pattern in order to avoid a situation where multiple adjacent memory strings MS are selected at the same time. This will be discussed in more detail later. Note that adjacent memory cells MS1 and MS2 in
The memory strings MS are arranged immediately either below bit lines BL or source lines SL with the column direction taken as their longitudinal direction. That is, both ends BE and SE in one memory string MS exist immediately below either one bit line BL or one source line SL.
Thus, as illustrated in
As illustrated in
Similarly, each connection wiring M0b is formed below each connection wiring M1b with the column direction taken as its longitudinal direction. The bottom surface of each connection wiring M0b is connected to an end BE (the upper end of a columnar portion CLmn). In addition, each connection wiring M1b is formed with the row direction taken as its longitudinal direction, and its bottom surface is electrically connected to a connection wiring M0b via a contact CT. The top surface of each connection wiring M1b is connected to a bit line BL via a contact CT. Note that the connection between each connection wiring M0b and each end BE may be provided via a contact.
In addition, although not illustrated in
With this configuration, a plurality of memory string MS (e.g., the memory strings MS0, MS1, MS2 in
Referring now to
As illustrated in
Referring now to
Upon application of these voltages, the read voltage Vread and the determination voltage Vref are also applied to the control gate electrodes of the memory transistors MTr5 to 8 in the memory string MS0 adjacent to the memory string MS1. However, in this memory string MS0, a ground potential Vss is applied to the selection gate line SG of the drain-side selection transistor SDTr (not illustrated in
Similarly, the memory string MS2 also shares four word lines WL with the memory string MS1, which word lines are applied with the read voltage Vread. As such, in the memory string MS2, the corresponding four memory transistors MTr are brought into conductive states. However, the remaining memory transistors MTr are not applied with the read voltage Vread or the like, and the corresponding source-side selection transistor SSTr is maintained in a non-conductive state. Again, no current path is formed in the memory string MS2.
As can be seen from the above operation, only one of a plurality of memory string MS can be selected arbitrarily that are formed along a pair of a bit line BL and a source line SL. In this embodiment, this operation is ensured by arranging the memory strings MS in a zig-zag pattern on a plane. In addition, only one of the memory strings MS allows read current to flow into one source line SL even if a multiple-bit read operation is performed by activating a plurality of bit lines BL at the same time. Therefore, this embodiment may suppress the potential floating of source lines SL as compared with the conventional technology where read current from a plurality of memory strings MS flows into one source line SL. As a result, this embodiment may reduce variations in the read current and providing a larger read margin. In addition, suppressing the potential floating of source lines SL may yield larger read current and reduce reading time.
Referring now to
In this case, as with conventional NAND-cell-type flash memory, the word line WL of the memory transistor MTr4 is applied with a program voltage Vpgm of not less than 20V, and the other word lines WL are applied with a pass voltage Vpass of on the order of 8V, Note that the bit lines BL are applied with a voltage depending on the write data (ground voltage Vss when writing “0”, or power supply voltage Vdd when writing “1”). Thus, these voltages are also applied to the memory strings MS0 and MS2 that are adjacent to the memory string MS1 and share the word lines WL with each other. However, since an off voltage is applied to the selection gate SG of the source-side selection transistor SSTr of the memory string MS1, the drain-side selection transistor SDTr of the memory string MS2 is also in a non-conductive state. Thus, the write operation is not performed in the memory string MS2. In the memory string MS0, the selection transistor (not illustrated in
Referring now to
However, this embodiment is different from the first embodiment in that each source line SL has a larger width (length in the row direction) than that of each bit line BL. That is, each source line SL has a width to accommodate two memory strings MS aligned in the row direction, which is about three times the width of each bit line BL. A plurality of memory string MS aligned in the row direction are arranged in a zig-zag pattern so that their respective ends are staggered with respect to each other in the column direction, which is the same as described in the first embodiment. In addition, the ends BE and SE of the memory strings MS are connected in the same way as described in the first embodiment.
According to this embodiment, each source line SL has a larger width and hence a smaller resistance, which may further suppress the potential floating of a source line SL in read operation.
Referring now to
The shapes and the arrangement of the word lines WL, the selection gate lines SG and so on in the memory cell array 12 are the same as the first embodiment, and so will not be described in detail below. The third embodiment is different from the above-described embodiments in that the back-gate lines BG are such wirings extending in the column direction and arranged in a stripe pattern at the same arrangement pitch as those of the bit lines BL and the source lines SL, rather than a plate-like wiring commonly connected to m×n memory strings MS.
In addition, as illustrated in
Referring now to
Referring now to
The bit lines BL are arranged at a certain arrangement pitch with the column direction taken as their longitudinal direction, and the source lines SL are also arranged at a certain pitch with the column direction taken as their longitudinal direction. Unlike the above embodiments, the bit lines BL and the source lines SL are not formed in the same layer; the source lines SL are provided in a lower layer below the bit lines BL. However, this embodiment is similar to the above embodiments in that the bit lines BL and the source lines SL are formed in parallel. In, addition, this embodiment is similar to the above embodiments in that a plurality of (in this figure four) memory strings MS are connected in parallel between a pair of a bit line BL and a source line SL. These four memory strings are connected to independent drain-side selection gate lines SGD1 to 4, respectively. The drain-side selection gate lines SGD1 to 4 are arranged with the row direction, orthogonal to the bit lines BL and the source lines SL, taken as their longitudinal direction. Accordingly, for example, a plurality of selected memory strings MS are still connected to different source lines SL when a read operation is performed by causing a plurality of bit lines BL to go high at the same time. Therefore, the read current cannot be reduced due to the potential floating of source lines SL, which may ensure a sufficient reading speed and provide a larger read margin.
[Others]
While embodiments of the present invention have been described, the present invention is not intended to be limited to the disclosed embodiments, and various other changes, additions or the like may be made thereto without departing from the spirit of the invention. For example, the following cases have been described in the above-described embodiments: where the word lines WL and the selection gate lines SG are shared between (commonly connected to) only those memory transistors along one columnar portion CLmn in a plurality of memory strings MS connected to a pair of a bit line BL and a source line SL (the first and second embodiments); and where all of the word lines WL and the selection gate lines SG are shared between the memory transistors, while only the back-gate lines BG being provided independently (the third and fourth embodiments). However, the present invention is not so limited. Other configurations may fall within the scope of the invention where a plurality of memory strings connected to a pair of a bit line and a source line can share at least some of the word lines or selection gate lines, and the voltage of some of the remaining wirings can be controlled independently, allowing arbitrary activation of only one of the plurality of memory strings.
In addition, the configuration to achieve an equivalent circuit as illustrated in
For example, the circuit as illustrated in the equivalent circuit of
In addition, the configuration as illustrated in the equivalent circuit of
In addition, while the above embodiments have been described in the context of adjacent memory strings MS being included in the equivalent circuits as illustrated in
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